Ok so you've had some major life changes recently - moving house to a radically different place, new(ish) partner, new baby (altered hormones/body image and the sleep deprivation that comes as part and parcel of this) and I would imagine massive logistics with making all these transitions with your older kids.
Social isolation is really hard especially in the context of all this change. Is there any chance of getting a time out for yourself? Say when DP is away could you take a few days and stay with anyone near to your old base? Take some time to go shopping and fill the days with some comfy company? It is not a permanent solution but may get you through the eye of the storm? Could the other kids hang out with their Dad/Mum or Grandparent for a few days to let you rest/refresh? I know with school starting this may be difficult but a few days off may not matter.
xxxx